Spin bath treatment



Patented Jan. 19 1954 IUNITE'D TEN T F ICE ai s- (01. 1=s--54 This. invention relates tothe production off-re- :generated' cellulose filaments bystherviscoseiprocwhereby regenerated cellulose materials ofi 'improved color may be obtained.

-,:Inathe production of artificial filamentssby the viscose process, celluiose'is treated with sodium hydroxideto convertitutoalkali cellulosey the alkali cellulose reacted with carbonrbisulfide to form. cellulose .xanthate and the 'cel1ulose: Xanthate then dissolved in 'aqueous-sodiumhydroxide to yield a. spinning .solutionawhich is extruded through a spinneret into an acid spin bath where itcoagulates or sets to form cellulose filaments. The.acid; spin bath employed; usually comprises a 10-12% aqueous solution. of sulfurioacid con taining about 18-24 sodium sulfate and a small amount oizincsulfate. In commercialspinning operations. the spin. bath is normally circulated in aclosed system. l The bath is-made ,uporiginally inonepart of..the system, pumpedtothe spin bath troughs .intowhich the viscose solutionis..ext1'uded,then sent .to'. a makeeup=zone ,whereit. is brought up to .the desired' strength, filtered and the rechargedspin.bathrecirculated to that part of the system lwhere t-heactual spinhing is efiected. Due. to the corrosive nature. of the sulfuric. .acid spin bath .solution,'.the entire circulation system is usually lined. with a material, such as lead, for example, which is strongly resistant to corrosion.

Although lead is so highly'advantageous as an acid-resistant (structural material that its use 'is practically universal, the presence-of lead incontact..with the acid spin bath permits :the-latter to pick .up varying amounts 0f soluble-leadcompounds. In turn, the-cellulose:materials-coagu lated in lead-containing spin baths-also pickup the. lead compounds present-. and, when the amount of lead in thespin bath 1s-:-above a-cen tam. minimum concentration, tne-cellulosematerials coag-ulatedein the. spilrbatn-rtendito become badly olscoloreu'. While-certain special-washingprocedures are 'eii'ecti've 1n removang auleastsome of. line discoloration, tnese"w asmng 'op'eratlons represent. an. aqClllllolflal' and: appreclab1e-item 1n the cost 01 production. :tslnce 101 has peen -nrm'ly eSI'aDflSHeCl that line Jipresence "Of "HBXUGSSlVG amounts, or clean. in: the .spmxbath: 1s 13681301131018 tor .tne. discoloration. wmcnznast oeemobsenvea m cellulose.- materials coaguiaueulin su'cn oatns,- tne removal. crimes lead-on a. reuuu61on. 1n tne:quan-' V a 2, tration appears to 'be' es'sential if-"spe'cial Washing pro'edures 'areto be elim'inatedj" While several methods for-theelimination or reductions of lead in-spin'baths havebeen'p'r'opesed, the are, howei/erye'ither-ineffective'or else unsatisfactory for c'omm'erciali application.

';It is; th'ereforewan important object of this'inven'tion to provide aneffilzient and economical procession the treatment ofspin" baths employed in" the produ'ction of -'cel1u'lose 6 materials 1 by the viscose F pro'cess and' "circulating in contact with lead whereby thei-le'ad content of said-'spiii'baths may be reduced to an innocuous concentration.

1 Anotherobjct'of-this invention is to efifect a reductioflin the amount'of' lead present in viscose process spin-baths to anon -discoloring concentration by a continuous treatment of the 'coiagulatingspiir 'bath'employed' While" the"same is losing" circulat'edfland fortifiedfor reuse.

A 'fur-tlier ob'ject ofthis i'nil'e'r'ition istlie provision' -of a rooess for the treatment of'lea'deontammg' -spi baths fe'ihployed in-the production of cellulos matei ial's-by the *vi'scose process whereby thelead is' -sp'arated rom the spin bath un -t e of a' precipitate-Whichinay be readily filtered irom-the' spin bath during recirculation.

"Other objeots of this invention will app'ea'r from the 'following detailed description. 7

I have ioundthat the"leadpi'esent' incontam-inated sulfuric acidspin' baths employed f or the production 0f cellulose 'materials by the i/iscost-process may be readily-removed "or "at least the a'mount presentreducedto a non-'discoloring concentration by co-pree'iizaitzifiaingthe lead from solution bytheadditionto'saidsoiution'oi a com poundof analk aline earth nietal. Upon addition of an alkalineearth metal compound to' the sulfuric" 301d spin -bath; said alkaline earth metal precipitates theriromas' the corresponding" sulfate. -Thexprecipitation oi I said alkaline earth metal sulriate i'rom solution causes a copreclpitation whereby the lead' suli'ate present coprecipitates with the alkaline earth metal'suh'ate; By adding" a sumcient amount of the alkaline earth metal compound to thespm bath as the same is circulated-' he' ariiou'ntor 'lead' press" u "r.my-' be readily ced toanon-mscoloixn tion. A ter the-"additi'onbi? the-ainah'ne earth metaleompeunaymes ln bath "maytheri be nlte'r'ed,-- -brought up to" i'er'igm anq 'tnen reused forthe"-Iurtner must-ion oseenmose materials Withoutany oan'ger'oi' producing discolored m'a-' teri als due to an-excessive -concentramon 'orlead. in the "spur bath.

tlty r ao present'xoa non mscolonngwoflcn- Exampies-- e1 alkalineearm maai"compellin which may be employed in carrying out my novel process for the reduction of lead in spin baths are the compounds of barium or strontium, for example. Preferably, the soluble compounds of alkaline earth metals are employed. Thus, as suitable compounds which may be added to the spin bath in accordance with my novel process to effect a reduction in the lead content of said spin bath, there may be mentioned barium chloride, barium hydroxide, barium oxide, strontium nitrate, strontium chloride and strontium acetate. These compounds may be added alone or in admixture with each other. A suspension of the insoluble barium carbonate may also be employed.

The amount of the soluble alkaline earth metal salt added to the spin bath may vary depending upon the amount of lead in the spin bath and the extent to which it is desired to reduce the amount of lead in said spin bath. The lead in the spin bath normally amounts to from about 4 to about 16 parts or more per million on the weight of the spin bath after the bath has been in use for several months and an equilibrium has been reached. The addition to the spin bath of 1 to parts, preferably 1 to 15, per million by weight of soluble barium or strontium compounds effectively reduces the lead content of the bath to as little as 0.3 parts per million on the weight of the spin bath. Optimum results are obtained employing soluble barium compounds, particularly barium chloride or barium hydroxide, as the precipitating agent in the removal of lead from the spin bath.

To be effective in removing lead from the spin bath as a coprecipitate with the alkaline earth metal sulfate precipitate formed upon addition of an alkaline earth metal compound to the spin bath, the alkaline earth metal compound must be added under such conditions as to result in the formation of a very finely divided dispersion of the corresponding sulfate. The very finely divided sulfate precipitate is then permitted to settle in the spin bath for a sufiicient time to allow the colloidal particles to agglomerate. The

precipitation of the alkaline earth metal sulfate F in finely divided form, followed by settling, allows the desired mixed crystal formation of lead sulfate and alkaline earth metal. sulfate to take place. The mixed crystal formation causes a coprecipitation of lead sulfate from the spin bath, which reduces the amount of lead sulfate in the spin bath to below its normal solubility. Preferably, the spin bath is maintained at a temperature of 40 to C. during the addition of the soluble salt whereby the initial colloidal precipitation takes place. Settling may be conveniently achieved by providing a baffled chamber of relatively large volume which permits the precipitate to be trapped by the baffles and the supernatant liquid continuously drawn ofi and recirculated.

In order further to illustrate my invention, but without being limited thereto, the following examples are given:

Example 1 An aqueous spin bath of a total volume of about 1,000 gallons containing about 12% by weight of sulfuric acid, 20% sodium sulfate and 0.9% by weight of zinc sulfate is continuously circulated at the rate of approximately 6.33 gals. per minute through a closed lead-lined system at a temperature of 50 C. and is employed for producing cellulose filaments by continuously extruding therein a suitable viscose solution employing the usual multi-hole spinneret. After effecting the coagulation of the viscose solution with the pro duction of regenerated cellulose filaments, the spin bath is filtered through a sand filter, refortifled to the optimum sulfuric acid, sodium sulfate and zinc sulfate content and recirculated to effect further coagulation of the viscose solution extruded thereinto. After circulation for '72 hours with the production of about 280 pounds of regenerated cellulose yarn, the spin bath is found to contain lead in an equilibrium amount of about 6.7 parts per million on the weight of the spin bath. The soluble lead compounds are picked up by the coagulating filaments and cause an appreciable amount of discoloration on the filaments. Only a part of the discoloration can be removed by washing. The yarn spun through said spin bath contains approximately parts per million of lead. After the lead content of said spin bath has reached an equilibrium value, a 25% by weight solution of barium chloride is continuously added to the spin bath as it leaves the zone wherein the coagulation of the filaments takes place, said addition being in an amount of about 5.3 cc. per minute. After the addition is continued for 48 hours, the concentration of the barium chloride solution added is reduced to 12.5% by weight and the addition made at a rate of about 10.6 cc. per minute. After 24 hours, the concentration of the solution added is reduced to 6.25% and the rate of addition held to about 21 cc. per minute. The absolute rate of addition of barium chloride is maintained substantially constant at about 40 to 50 parts per million by Weight on the weight of the spin bath circulated through the system. The addition of the 6.25% by weight solution is continued at about 21 cc. per minute for about 1 week and at that time the lead content of the bath is found to be stabilized at about 0.6 parts per million. The spin bath is allowed to settle after the barium chloride addition and any of the agglomerated barium sulfate precipitate remaining in the supernatant liquid is continuously filtered from the spin bath as the same is circulated through the system. The color of the yarn obtained when the lead content of the spin bath is held to 0.6 part by weight per million parts of spin bath is found to be substantially improved by the removal of the lead and special washing procedures may be entirely eliminated Without any substantial efiect on yarn color.

Example II An aqueous spin bath of total volume of about 53,000 gallons, containing approximately 10% by weight of sulphuric acid, 22% by weight of sodium sulfate and .9% by weight of zinc sulfate, is continuously circulated through a closed leadlined' system at a circulating rate of approximately 1200 gallons per minute. This spin bath is employed for producing viscose yarn by continuously extruding therein a suitable viscose solution employing the usual multi-hole spinneret. After effecting the coagulation of the viscose solution with the production of regenerated filaments, the spin bath, filtered through a sand filter is refortified to the optimum sulfuric acid, sodium sulfate and zinc sulfate contentand recirculated to effect further coagulation of the viscose solution extruded thereinto. On reaching equilibrium with the lead-lined system, this spin bath is found to contain 15 p. p. m. of lead. The lead compounds are picked up by the coagulating filaments and cause an appreciable.

amount of discoloration. After the normal type 15 .p; p. based on' th'e quantity-of spiirbath circulated through the system The barium hw droxide is added under conditions of violent agitation. During the first 12 hours, 132 pounds of barium hydroxide are added. This reduces the-E lead content of the spin bath from 15 p. p. m. to 6 p. p. m. During the next 12 hour period, 87 pounds of barium hydroxide are added at the rate of approximately p. p. m. on the weight of the spin bath circulated. This results in a reduction in the lead content of the spin bath to 2 p. p. m. During the next 12 hour period, 66 pounds of barium hydroxide are added at the rate of approximately 7 p. p. m. on the weight of the spin bath circulated. Then for 12 hours the barium hydroxide addition is maintained at 5 p. p. m., which results in a reduction of the lead content of the spin bath to approximately 2.5 p. p. m. The addition of barium hydroxide is then reduced to approximately 2.5 p. p. m., based on the weight of the spin bath circulated, and maintained at this level for 16 days, at the end of which time the lead content of the spin bath is found to be reduced to approximately 1.2 p. p. m. The addition of barium hydroxide is increased to 3.75 p. p. m. for 6 days, then reduced to 1.25 p. p. m. for 20 days. By the end of this period the lead content of the spin bath reached a value of less than 0.5 p. p. m. The yarn spun through the spin bath containing this low concentration of lead is found to contain approximately 4 p. p. m. of lead and .does not exhibit the discoloration characteristic of yarns spun through spin baths containing several p. p. m. of lead.

Example III An aqueous spin bath of a total volume of about 74,000 gallons, containing approximately 12% by weight of sulfuric acid, 20% of sodium sulfate and 0.9% of zinc sulfate, is continuously circulated through a closed lead-lined system at a rate of approximately 4300 gallons p. m. This spin bath is employed as described in Example II. To this spin bath, now containing an equilibrium concentration of '7 p. p. m. of lead, is added a 5% solution of barium hydroxide, maintained at 40 C. at the rate of 2.5 p. p. m., based on the quantity of spin bath circulated through the system. The barium hydroxide is added under conditions of violent agitation. During the first 12 hours the lead content of the spin bath is reduced to 2 p. p. m. The addition of barium hydroxide is then increased to 5 p. p. m., and maintained at approximately this concentration for 16 days. By this time, the lead content of the spin bath is found to be reduced to less than 0.5 p. p. m. The addition of barium hydroxide is then reduced to 2.5 p. p. m. and maintained at this level for several days. The lead content of the spin bath remains less than 0.5 p. p. m. The marked discoloration characteristics of the yarn, spun prior to the addition of barium hydroxide to the spin bath disappears by the tim the lead content of the spin bath is below 1 p. p. m.

Example IV Employing a 5% aqueous solution of strontium fil a a e M9911 Y 1. 1-In -a process fo r the production or regenerated dell ulo se wherein viscose spinning solution is extruded into a spin bath comprising an aqueous solution of sulfuric acid, sodium sulfate and zinc sulfate for coagulating said spinning solution, in which process the spin bath is circulated through and outside the coagulating zone thereby coming into contact with metallic lead equipment, causing said spin bath to become contaminated with lead, the improvement which comprises adding an alkaline earth metal compound, which reacts with said spin bath to produce an alkaline earth metal sulfate, to said circulating spin bath, at a point removed from the coagulating zone and under such conditions as to produce an alkaline earth metal sulfate in finely divided form which precipitates and causes the co-precipitation of the lead sulfate in said spin bath, and removing the precipitate whereby the amount of lead contaminant is diminished and the tendency of the regenerated cellulose to discolor is reduced.

2. The process of claim 1 in which the alkaline earth metal of the alkaline earth metal compound is selected from the group consisting of strontium and barium.

3. Process of claim 1 in which the amount of the alkaline earth metal compound added to the spin bath is 1 to 50 parts per million based on the weight of the spin bath.

d. In a process for the production of regenerated cellulose wherein viscose spinning solution is extruded into a spin bath comprising an aqueous solution of sulfuric acid, sodium sulfate and zinc sulfate for coagulating said spinning solution, in which process the spin bath is continuously circulated through and outside the coagulating zone thereby coming into contact with metallic lead equipment, causing said spin bath to become contaminated with lead, the improvement which comprises adding with agitation to said circulating spin bath, at a point removed from the coagulating zone, an alkaline earth metal compound which reacts with said spin bath to produce an alkaline earth metal sulfate which precipitates in finely divided form and causes the co-precipitation of the lead sulfate in said spin bath, and removing the precipitate whereby the amount of lead contaminant is diminished and the tendency of the regenerated cellulose to discolor is reduced.

5. The process of claim 4 in which the alkaline earth metal of the alkaline earth metal compound is selected from the group consisting of strontium and barium.

6. Process of claim 4 in which the amount of the alkaline earth metal compound added to the spin bath is 1 to.50 parts per million based on the weight of the spin bath.

7. Process according to claim 4 in which the alkaline earth metal compound is barium hydroxide.

2,666,684 7 8 8. Process according to claim 4 in which the FOREIGN PATENTS alkaline earth metal compound is barium chlo- Number Country Date ride- 36 4 1932 RUSSELL O. DENYES. 6, 29 Great Britain Feb 4,

OTHER REFERENCES Journal American Chemical Society, vol. 60, 1938, pages 197-201.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,547,111 Finn July 21, 1 2 1,689,036 Leiss Oct. 23, 1928 2,326,592 Wicker Aug. 10, 1944 

1. IN A PROCESS FOR THE PRODUCTION OF REGENERATED CELLULOSE WHEREIN VISCOSE SPINNING SOLUTION IS EXTRUDED INTO A SPIN BATH COMPRISING AN AQUEOUS SOLUTION OF SULFURIC ACID, SODIUM SULFATE AND ZINC SULFATE FOR COAGULATING SAID SPINNING SOLUTION, IN WHICH PROCESS THE SPIN BATH IS CIRCULATED THROUGH AND OUTSIDE THE COAGULATING ZONE THEREBY COMING INTO CONTACT WITH METALLIC LEAD EQUIPMENT, CAUSING SAID SPIN BATH TO BECOME CONTAMINATED WITH LEAD, THE IMPROVEMENT WHICH COMPRISES ADDING AN ALKALINE EARTH METAL COMPOUND, WHICH REACTS WITH SAID SPIN BATH TO PRODUCE AN ALKALINE EARTH METAL SULFATE, TO SAID CIRCULATING SPIN BATH, AT A POINT REMOVED FROM THE COAGULATING ZONE AND UNDER SUCH CONDITIONS AS TO PRODUCE AN ALKALINE EARTH METAL SULFATE IN FINELY DIVIDED FORM WHICH PRECIPITATES AND CASUES THE CO-PRECIPITATION OF THE LEAD SULFATE IN SAID SPIN BATH, AND REMOVING THE PRECIPITATE WHEREBY THE AMOUNT OF LEAD CONTAMINANT IS DIMINISHED AND THE TENDENCY OF THE REGENERATED CELLULOSE TO DISCOLOR IS REDUCED. 